The heart of a computer is a magnetic hard disk drive (HDD) which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk, and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions. The volume of information processing in the information age is increasing rapidly. In particular, there is a desire for HDDs to store more information in its limited area and volume. A technical approach to meet this desire is to increase the capacity by increasing the recording density of the HDD. To achieve higher recording density, further miniaturization of recording bits is effective, which in turn typically requires the design of smaller and smaller components.
Increased density is essential for increasing the capacity of magnetic disk devices and making these devices more compact. The recording density of a magnetic disk depends, among other things, on magnetic film characteristics of the magnetic recording medium (coercive force, film thickness, etc.), magnetic head characteristics (frequency characteristics, gap length, etc.), and spacing between the magnetic film of the magnetic recording medium and the magnetic head (referred to below as the “magnetic spacing”).
One method of increasing the recording density of a magnetic disk involves a decrease in the medium noise caused by reducing the magnetization inversion of the magnetic recording medium. Conventional magnetic recording media employ a structure in which the ferromagnetic crystal grains which form the magnetic layer are separated by a non-magnetic material which is already contained in the recording layer.
Magnetic recording media have been proposed in which the magnetic recording density is increased by controlling these separating regions more actively. Research and development are currently focused on discrete track media in which processing is carried out in order to provide separation between recording tracks, and also bit patterned media in which processing is carried out in order to provide separation between recording bits. In both cases, the technology for forming separating regions is one factor in increasing the density. For discrete track media, for example, a type of magnetic film processing has been proposed as a technology for forming separating regions, in which recording regions and separating regions are produced on the recording layer by masking the recording layer and etching the regions to be separated. The space between the magnetic recording medium and the magnetic head (referred to below as the “flying height”) has been reduced to around 10 nm, and with this kind of discrete track medium the planarity of the surface is a factor in achieving favorable recording and reproduction characteristics by stabilizing the flying height of the magnetic head. It is therefore preferable for the separating regions to be filled with a non-magnetic material, and for any excess filler present on the recording regions to be removed in order to planarize the top surface of the recording regions and separating regions. Diamond-like carbon (DLC) is preferably used as a filler, according to disclosures in Japanese Unexamined Patent Application Publication No. 2003-109210, for example. It should be noted that DLC is also used as an overcoat for may magnetic recording media. Chemical vapor deposition (CVD) employing hydrocarbon gas may be used with DLC. Furthermore, one method for removing excess filler in order to planarize the surface involves a dry process such as ion beam etching (IBE) or reactive ion beam etching, or a wet process such as chemical mechanical polishing (CMP). It should be noted that with wet processes, such as CMP, residual microparticles often have an adverse effect on the ability of the magnetic head to float above the medium and the electromagnetic conversion characteristics, and therefore dry processes are often selected. For example, Japanese Unexamined Patent Application Publication No. 2007-272948 discloses a method in which separating regions are filled with amorphous carbon formed by sputtering using a graphite target and the surface is then planarized by etching, after which a DLC protective layer is formed by chemical vapor deposition (CVD).
DLC is used as an overcoat for magnetic recording media according to the examples above. Additionally, the magnetic spacing is reduced in order to increase the density, and high hardness and high density DLC is formed to around several nm in order to meet corrosion resistance and durability product performance parameters. If the hydrogen content of the DLC is low and the sp3 ratio is high, it tends to exhibit properties of high strength at high density. However, the filler for the separating regions formed more thickly than the regions need for an overcoat, and therefore problems arise, such as peeling, when the separating regions are filled with DLC which has a low hydrogen content. Furthermore, a DLC film is grown in accordance with the pattern of the recording layer, and therefore there is a large difference in level after the separating regions have been filled. Furthermore, even if the excess filler is removed in a dry process in which mechanical polishing is carried out, like in CMP, the surface cannot be adequately planarized.
As a result, there are problems in that the magnetic head does not fly stably during operation. It should be noted that the difference in level in the unevenness on the surface tends to decrease as the film of filler which is formed becomes thicker, and it is possible to keep the difference in level in the unevenness down to a small size after the separating regions have been filled by forming the filler thickly. However, if the filler is formed thickly, more time is needed for the process of filling the separating regions and for the process of removing the excess filler, which reduces production efficiency.
Furthermore, not enough consideration has been given to sliding reliability in conventional magnetic recording media, with regard to reducing the flying height of the magnetic head, something which is useful to increase the recording density of the media. That is to say, contact between the magnetic head and the magnetic recording medium which occurs as the flying height of the magnetic head is reduced may cause damage such that the data recorded on the magnetic recording medium cannot be read: this is referred to as “crash.” For this reason, the DLC overcoat surface of the magnetic recording medium is coated with a lubricant, which reduces the shear force of the magnetic head, in order to reduce wear of the magnetic head and the magnetic recording medium, in such a way that crash does not occur even if the two come into contact. However, the magnetic recording medium rotates at a high speed of at least 5400 rpm, for example, and therefore a phenomenon occurs whereby as the lubricant is scattered (lubricant film thickness becomes thinner than that of initial lubricant film thickness), the capacity for reducing the shear force is reduced, and the wear resistance deteriorates. According to recent practice, a lubricant having polar groups at the terminals is often applied in order to provide a reasonable trade off between wear resistance and a reduction in scattering of the lubricant caused by the rotation of the magnetic recording medium. However, even though lubricants having polar groups are not scattered, they have high affinity to the DLC overcoat, and therefore there is a decrease in their ability to reduce the shear force when there is contact with the magnetic head. Considering the contact between the magnetic recording medium and the magnetic head which accompanies the reduction in the flying height of the magnetic head, there are problems in terms of compatibility between the capacity to reduce the shear force and reducing the tendency of the lubricant to scatter.
Japanese Unexamined Patent Application Publication No. 2007-272948 discloses a patterned medium in which separating regions are filled with amorphous carbon and a DLC overcoat is formed on a magnetic film by CVD, but the following problems arise with the methods of formation. Firstly, when the separating regions are filled with amorphous carbon using sputtering and the pattern pitch is made finer in order to increase the density, there is a strong possibility that voids will form within the separating regions during the sputtering which provides poor coverage of the difference in level, and corrosion will most likely occur over time. Secondly, not enough consideration has been given to sliding reliability in the magnetic recording media, with regard to reducing the flying height of the magnetic head, something which is useful to increase the density.
Accordingly, a method of producing a magnetic recording medium which provides high density recording while alleviating or eliminating the problems associated with prior attempts would be beneficial.